Garlic should be peeled fresh for maximum aroma. Pre-peeled garlic loses its volatile compounds, which are responsible for its characteristic scent and flavor.
The aroma of garlic comes from a compound called allicin, which is formed when alliin (a stable, odorless compound) comes into contact with the enzyme alliinase. This reaction occurs when garlic cloves are crushed, chopped, or otherwise damaged. When garlic is pre-peeled, it's often stored for extended periods, which allows these volatile compounds to degrade. This degradation is accelerated by exposure to air and light. Freshly peeled garlic, on the other hand, releases its full aromatic potential immediately upon preparation, resulting in a more intense and flavorful experience. The oils responsible for the garlic's flavor are also more readily available when freshly peeled and prepared.
To easily peel garlic, smash the clove gently with the flat side of a knife. This loosens the skin, making it much easier to remove. You can also place the cloves in a jar, seal it, and shake vigorously for a few seconds to separate the skin.